This invention relates to tooth forming machines which displace metal through a cold forming process and are capable of producing the finished part more economically than traditional methods of removing metal, such as cutting. More particularly, this invention is directed to an improved segmented rack for such machines which permits the removal of damaged tooth sections.
Typical cold rolling machines which form splines, serrations, and similar teeth by rolling a cylindrical workpiece between dies moving in opposite directions are described in U.S. Pat. Nos. 2,994,237 to H. Pelphrey; 2,995,964 to J. C. Drader; 3,015,243 to J. C. Drader and 3,818,964 to Blue. With these machines, pairs of elongated racks or dies are used to produce a particular part, and it is desirable that each set of racks normally produce several thousand splines or the like before regrinding of the racks is required. Unfortunately, the severe work environment experienced by these racks results in excessive stress risers and accompanying a cracking of some of the teeth thereof through fatigue-type failures. Since these racks cost up several thousand dollars, failure are extremely costly. Furthermore, when these present racks fail, sufficient material must be removed for the entire length of the rack to get below the fatigue-affected zone. Following this, new teeth are ground on the full length of the rack.
Another problem with current racks is that the rack is made of relatively costly tool steel and requires many pounds of this relatively expensive material. For example, present racks use 165-375 lbs. of tool steel for a 36" rack and 275-450 lbs. for a 48" rack.
Furthermore, to anticipate the breakage that will occur to the teeth of these current racks, a large number of racks must be maintained and stored. This storage requires a great deal of space and also ties-up capital.